Sweat sensing technologies have enormous potential for applications ranging from athletics to neonatology, to pharmacological monitoring, to personal digital health, to name a few applications. Sweat contains many of the same biomarkers, chemicals, or solutes that are carried in blood and can provide significant information enabling one to diagnose illness, health status, exposure to toxins, performance, and other physiological attributes even in advance of any physical sign. Furthermore, sweat itself, the action of sweating, and other parameters, attributes, solutes, or features on, near, or beneath the skin can be measured to further reveal physiological information.
If sweat has such significant potential as a sensing paradigm, then why has it not emerged beyond decades-old usage in infant chloride assays for Cystic Fibrosis or in illicit drug monitoring patches? In decades of sweat sensing literature, the majority of practitioners in the art use the crude, slow, and inconvenient process of sweat stimulation, collection of a sample, transport of the sample to a lab, and then analysis of the sample by a bench-top machine and a trained expert. This process is so labor intensive, complicated, and costly that in most cases, one would just as well implement a blood draw since it is the gold standard for most forms of high performance biomarker sensing. Hence, sweat sensing has not emerged into its fullest opportunity and capability for biosensing, especially for continuous or repeated biosensing or monitoring. Furthermore, attempts at using sweat to sense “holy grails” such as glucose have not yet succeeded to produce viable commercial products, reducing the publicly perceived capability and opportunity space for sweat sensing.
Of all the other physiological fluids used for biological monitoring (e.g., blood, urine, saliva, tears), sweat has arguably the least predictable sampling rate in the absence of technology. However, with proper application of technology, sweat can be made to outperform other non-invasive or less invasive biofluids in predictable sampling.
For example, it is difficult to control saliva or tear rate without negative consequences for the user (e.g., dry eyes, tears, dry mouth, or excessive saliva while talking). Urine is also a difficult fluid for physiological monitoring, because it is inconvenient to take multiple urine samples, it is not always possible to take a urine sample when needed, and control of biomarker dilution in urine imposes further significant inconveniences on the user or test subject.
Many of the drawbacks and limitations stated above can be resolved by creating novel and advanced interplays of chemicals, materials, sensors, electronics, microfluidics, algorithms, computing, software, systems, and other features or designs, in a manner that affordably, effectively, conveniently, intelligently, or reliably brings sweat sensing technology into intimate proximity with sweat as it is generated. With such an invention, sweat sensing could become a compelling new paradigm as a biosensing platform.
In particular, sweat sensors hold tremendous promise for use in workplace safety, athletic, military, and health care settings. For workplace safety and military applications, a sweat sensing device worn on the job and connected to a computer network via a reader device, such as a smart phone or other portable or stationary device, could relay crucial data about physiological conditions, or the presence of prohibited substances in the bloodstream. In health care settings, sweat sensors may continuously monitor the health of individuals, for example, patients who are restricted to bed rest or participating in a clinical trial, and communicate to a reader device or computer network, which would then compare collected data to threshold readings and alert caregivers if the individual is in need of intervention.
For these applications to be effective, however, it is crucial that a targeted individual is wearing the proper sweat sensor device, and that the device is operational. Sweat sensor devices may be deployed in various internal configurations, with devices configured for detecting a specific analyte or a group of analytes, depending on the application. If a device is placed on a different individual than the target individual, the collected information will be inapplicable to the target individual. Or, if a target individual is wearing the incorrect device for a particular application, the desired information may not be collected. Likewise, a device that has inadequate contact with the skin, or that is otherwise inoperable due to electronic or other malfunction, will not effectively collect sweat and detect the targeted analytes.